JPS57573A - Optical detector - Google Patents

Abstract

PURPOSE:To prevent opened or closed condition from mistaking with an auxiliary means without affected with electrical noise and without fear of decomposition by detecting opened or closed condition of a window or a door as a part of the loop of an optical fiber. CONSTITUTION:A light from a light emitting element 7 drived with a driving circuit 8 is radiated to the end surface 3a of one side of an optical guide 3 through an optical fiber 5. A light radiated from the other end surface 3b of the optical guide 3 is injected to the one end surface 4b of an optical guide 4 and is radiated to an optical fiber 6 from the other end surface 4a of the optical fiber 4. The light is detected with a light detecting element 9 via the optical fiber 6, is amplified with an amplifying circuit 10 and is processed with a processing circuit 11 according to the purpose. When the light, through loops 5, 3, 4, 6, is detected beyond a certain criterion with the amplifying circuit 10, a window or a door 1, 2 is closed, when it is opened, the light does not form a loop and becomes lower than a certain criterion at the amplifying circuit 10 and further, for instance, alarmed with the processing circuit 11.